1. Field of the Invention
This invention relates to a semiconductor composite element which is employed in equipment such as an inverter device, and in which abnormal conditions of overcurrent, control voltage reduction, and overheat are detected, and different abnormality signals are outputted according to the respective abnormal conditions thus detected, and to a method of detecting abnormal conditions in an inverter device having the semiconductor composite element.
2. Description of the Background Art
FIG. 5 is a block diagram showing the internal arrangement of a conventional semiconductor composite element. In FIG. 5, reference symbol 20 designates the semiconductor composite element; 21a, a positive-side control power source terminal; 21b, a negative-side control power source terminal; 22a, a positive-side control common terminal; 22b, a negative-side control common terminal; 23a, a positive-side control signal input terminal; 23b, a negative-side control signal input terminal; 24a, a positive-side abnormality signal output terminal; 24b, a negative-side abnormality signal output terminal; 25a, a positive-side DC power input terminal; 25b, a negative-side DC power input terminal; 26, an AC power output terminal; 27a, a positive-side semiconductor switching element which is a transistor; and 27b, a negative-side semiconductor switching element which is also a transistor. Further in FIG. 5, reference symbol 28a denotes a positive-side diode; 28b, a negative-side diode; 29a, a positive-side transistor current detector; 29b, a negative-side transistor current detector; 30a, a positive-side transistor drive circuit; 30b, a negative-side transistor drive circuit; 31a, a positive-side transistor overcurrent protection circuit; 31b, a negative-side transistor overcurrent protection circuit; 32a, a positive-side control supply voltage reduction protecting circuit; 32b, a negative-side control supply voltage reduction protecting circuit; 33, a temperature detector for detecting a temperature of the semiconductor composite element 20; 34, an overheat protection circuit; 35, a first logical OR circuit which produces an output signal upon reception of any one of the output signals of the positive-side transistor overcurrent protection circuit 31a and of the positive-side control supply voltage protection circuit 32a; and 36, a second logical OR circuit which produces an output signal upon reception of any one of the output signals of the negative-side transistor overcurrent protection circuit 31b and of the negative-side control supply voltage protection circuit 32b.
In the conventional semiconductor composite element 20 thus organized, control signals which do not turn on the positive-side transistor 27a and the negative-side transistor 27b at the same time are applied to the positive-side and negative-side control signal input terminals 23a and 23b, respectively, so that the transistors 27a and 27b are alternately turned on and off through the positive-side transistor drive circuit 30a and the negative-side transistor drive circuit 30b, to provide AC power at the AC power output terminal 26 whereby AC current flows in the transistors.
In this operation, the currents flowing in the positive-side transistor 27a and the negative side transistor 27b are detected by the positive-side current detector 29a and the negative-side current detector 29b, respectively. The positive-side overcurrent protection circuit 31a and the negative-side overcurrent protection circuit 31b determine whether or not the currents thus detected are abnormal, i.e. larger than a predetermined value. When detecting an overcurrent abnormality, the positive-side overcurrent protection circuit 31a (or negative-side overcurrent protection circuit 31b) supplies an abnormality signal to the positive-side transistor drive circuit 30a (or negative-side transistor drive circuit 30b) connected thereto. Upon reception of the abnormality signal, the positive-side transistor drive circuit 30a (or negative-side transistor drive circuit 30b) turns off the positive-side transistor 27a (or negative-side transistor 27b) to cut off the current irrespective of the control signal applied to the positive-side (or negative-side) control signal input terminal 23a (or 23b). At the same time, the positive-side overcurrent protection circuit 31a (or negative-side overcurrent protection circuit 31b) supplies the abnormality signal through the first logical OR element 35 (or second logical OR element 36) to the positive-side abnormality signal output terminal 24a (or negative-side abnormality signal output terminal 24b.
On the other hand, a control supply voltage applied between the positive-side control power source terminal 21a and the positive-side control common terminal 22a, and a control supply voltage applied between the negative-side control power source terminal 21b and the negative-side control common terminal 22b are read by the positive-side control supply voltage reduction protecting circuit 32a and the negative-side control supply voltage reduction protecting circuit 32b, respectively, so that it is determined whether or not the control supply voltages are abnormal being smaller than a predetermined value. When an abnormality occurs involving a control supply voltage reduction, in a manner similar to the above-described overcurrent detection, the positive-side control supply voltage reduction protecting circuit 32a (or negative-side control supply voltage reduction protecting circuit 32b) supplies an abnormality signal to the positive-side transistor drive circuit 30a (or negative-side transistor drive circuit 30b). Upon reception of the abnormality signal, the positive-side transistor drive circuit 30a (or negative-side transistor drive circuit 30b) turns off the positive-side transistor 27a (or negative-side transistor 27b) to cut off the current irrespective of the control signal applied to the positive side (or negative side) control signal input terminal 23a (or 23b). At the same time, the positive-side control supply voltage reduction protecting circuit 32a (or negative-side control supply voltage reduction protecting circuit 32b) supplies the abnormality signal through the first logical OR element 35 (or second logical OR element 36) to the positive-side abnormality signal output terminal 24a (or negative-side abnormality signal output terminal 24b).
The temperature of the semiconductor composite element 20 is detected by the temperature detector 33. The overheat protection circuit 34 determines whether or not the temperature thus detected is abnormal, i.e., higher than a predetermined value. When detecting an overheat abnormality, the overheat protection circuit 34 supplies an abnormality signal to the negative-side transistor drive circuit 30b. Upon reception of the abnormality signal, the negative-side transistor drive circuit 30b turns off the negative-side transistor 27b to cut off the current irrespective of the control signal applied to the negative-side control signal input terminal 23b. At the same time, the overheat protection circuit 34 supplies the abnormality signal through the second logical OR element 36 to the negative-side abnormality signal output terminal 24b.
As was described above, in the conventional semiconductor composite element, in order to detect three abnormal conditions of overcurrent, control supply voltage reduction and overheat, the detected current, voltage and temperature are compared with the predetermined values, respectively, to determine whether or not they are abnormal; and when it is determined that any one of the current, voltage and temperature is abnormal, the abnormality signal is outputted to eliminate the abnormal condition. However, the semiconductor composite element involves a problem in that the particular abnormal condition cannot be identified from the abnormality signal thus outputted.